o2 Sensor CEL

So I have a b16 swap into my 1990 Civic hatch. DC-Sports 4-2-1 Header with one o2 sensor. I have the 2nd one wired from the ECU to the 1 and only o2 sensor. After a hard pull I will get a CEL light for the O2 or when I am at high rev's and let off the gas and coast it will give me a CEL for the o2. Should I have a 2nd bung installed somewhere on the header and install a 2nd O2 or is something else wrong?